Lyman-alpha observations of astrospheres

TL;DR

This paper discusses how Lyman-alpha observations of hydrogen walls around stars can measure stellar mass-loss rates and explores their relation to X-ray emissions, highlighting key challenges.

Contribution

It introduces a technique using Lyman-alpha absorption to determine stellar mass-loss rates and offers a new perspective on their connection with X-ray emissions.

Findings

Hydrogen wall absorption is a viable method for measuring stellar mass-loss rates.

A proposed relation between mass-loss rates and stellar X-ray emission.

Identification of critical issues in interpreting Lyman-alpha observations.

Abstract

Charge-exchange reactions between outflowing stellar wind protons and interstellar neutral hydrogen atoms entering a stellar astrosphere produce a region of piled-up-decelerated neutral hydrogen called the hydrogen wall. Absorption by this gas, which is observed in stellar Lyman-alpha emission lines, provides the only viable technique at this time for measuring the mass-loss rates of F-M dwarf stars. We describe this technique, present an alternative way for understanding the relation of mass-loss rate with X-ray emission, and identify several critical issues.